1. Field of the Invention
The present invention relates generally to an information storage device and a servo gain compensating method of compensating a servo gain when in a seek operation and in a positioning process in the information storage device for reading or reading/writing information from and to a storage medium by a head, and more particularly to an information storage device and a servo gain compensating method of setting a servo gain corresponding to a measured temperature.
2. Description of the Related Art
An information storage device such as a magnetic disk device, etc. has been widely utilized as a storage device of a computer, etc. This type of information storage device has a servo loop for driving an actuator in accordance with position signal read from the head.
A scatter in terms of characteristics of a magnet and a coil of a voice coil motor (VCM) for moving the magnetic head, might be a factor for causing problems in a loop gain of a servo control system. Further, the scatter in gain of a control loop system circuit of a power amplifier, etc. also leads to a scatter in the loop gain of the servo control system. The scatter in the characteristic of the VCM and the scatter in the gain of the control system circuit may be integrated and conceived as a scatter in a servo loop gain of the control system.
In the magnetic disk device, the servo control is executed by compensating the above scatter (a gain compensation) when in the seek operation and in the positioning process on a target track. This servo gain value changes depending on an environment temperature of the device, and hence there must be a necessity for compensating the servo gain at an interval of a fixed time (5 min-10 min).
A calibration seek may be a general method as the one described above. According to the calibration seek, a drive current having a fixed value flows to the VCM for a fixed period of time, thereby executing a seeking process of the VCM. This method is that when in this seeking process, a quantity of displacement is measured from the positional information of the magnetic head, and a servo gain is measured based on the quantity of displacement. According to this calibration seek method, a precise servo gain value at that point of time can be measured. However, the seek operation is carried out, during which there is a necessity for having a host request wait. Therefore, a technology of compensating the servo gain without having the host request wait is needed.
FIG. 7 is a diagram showing a construction in the prior art. FIG. 8 is an explanatory diagram showing the prior art.
As illustrated in FIG. 7, a magnetic disk drive 91 includes a magnetic disk 92 and a magnetic head 90. The magnetic disk 92, on which a servo signal is recorded per sector, is rotated by a spindle motor 93. The magnetic head 90 reads and writes information from and to the magnetic disk 91.
The magnetic head 90 is moved in a track traversing direction on the magnetic disk 91 by a voice coil motor (VCM) 98. A control circuit 96 detects a present position of the head in accordance with a position signal given from the magnetic head 90, and generates a control value corresponding to a distance from a position to be sought.
For compensating scatters in characteristics of the VCM 98 and of the power amplifier 95, the control value is multiplied by the servo gain value. A drive value is outputted to the power amplifier 95, thereby driving the VCM 98.
This servo gain value changes depending on the temperature. A parameter table stored with the servo gain values at the respective temperatures is therefore prepared. This parameter table is, as shown in FIG. 8, stored with the servo gain value at every temperature. Further, the magnetic disk drive 91 is provided with a temperature sensor 94 for detecting a temperature of the drive 91.
In such a construction, the control circuit 96 periodically measures the temperature of the drive through the temperature sensor 94. Then, the control circuit 96 obtains a servo gain from the measured temperature referring to the parameter table in the memory 97. The servo control is executed based on this servo gain.
Thus, according to the prior art, the servo gain is compensated to a servo gain value corresponding to the temperature of the device without performing the calibration seek.
There arise, however, the following problems inherent in the prior art.
With downsizing of the magnetic disk device, the magnetic disk device is built in an electronic appliance such as a portable computer etc. In this case, the magnetic disk device receives heat from other units (such as, e.g., a host processor and a display unit) of the electronic appliance. These other units emit heat when operated but do not emit heat when not operated.
Therefore, the environment temperature of the magnetic disk device changes. The small-sized magnetic disk device has a small thermal capacity, and hence the temperature might change depending on the environment temperature. The temperature sensor measures the characteristics of the VCM and of the power amplifier from the temperature of the device. If the environment temperature changes abruptly, the characteristics of the VCM and of the power amplifier do not follow up the change in the temperature.
Accordingly, when using the servo gain in the table created on the assumption of the temperature change due to the emission of heat from the VCM and the power amplifier, the problem is that the servo gain can not be compensated to the servo gain value suited to the characteristics of the VCM and the power amplifier.